1. Field of the Invention
The present invention relates to a method and a device for checking a joint formed in an electronic component, and more particularly to the method and the device which are capable of checking the joint of an electronic component based on the comparison of the information such as a form and a temperature distribution of a soldered portion regarded as a plane on an electronic circuit board.
2. Description of the Prior Art
It has been likely that the joints of an electronic component, in particular, the soldered portions on an electronic circuit board are often made defective. To overcome the occurrence of these defective soldered portions, various proposals for checking the joint have been made.
For example, there may be referred to as the technique of "Method and Device for Checking joint" disclosed in Japanese Patent Laid-Open No. 60-73347. The checking method and device take the steps of heating an object having a joint to be checked, measuring a radiation temperature of the heated portion from radiated infrared ray, and determining whether or not the joint is defective based on the measured result of the temperatures.
Concretely, it is measured how a temperature of the heated portion is changed for a short time. The atmosphere condition (surface condition of an object to be checked and others) of the object to be checked is measured on the basis of the temperature change for a short time to which the defective portion gives no influence. At a time, it is measured how a temperature of the heated portion is changed for a relatively long time. The change for a long time is influenced by the defective joint. Hence, it is determined whether or not the joint is defective on the basis of the the long time changed temperature amended on the atmosphere condition.
That is to say, this checking method uses the phenomenon that a normally soldered portion has so low heat resistance as not causing a large temperature rise but a incompletely soldered portion has so high heat resistance as causing a large temperature rise for checking the soldered joint. The foregoing prior art is improved in that the influence of the soldered surface state is considered for measuring the long time changed temperature.
As another prior art, there may be referred to as the technique of "Device for Checking Soldered Portion of Component mounted on Surface" disclosed in Japanese Patent Laid-Open No. 62-237346.
This device operates to heat the opposite surface to the actual component-mounted surface of an electronic circuit board, gauge a surface temperature of a soldered terminal component from the actual component-mounted surface, measure a temperature change of the soldered component after being heated for a constant time by a heater, and determining whether or not the soldered portion is defective.
FIG. 19 is a view showing the concept of this device. When a heater 104 heats a circuit board 101 from the rear side, a solder 103 is heated through a copper foil pattern 101a of the circuit board. A temperature measure unit 105 serves to measure the heat conductive state of the solder for a constant time from the start of heating. Based on this output, the determining unit 106 serves to determine whether or not the solder is defective.
The former prior art operates to measure the on-time change of a temperature of one spot of a joint and determine whether or not the joint is defective based on the temperature change. The latter prior art operates to measure the temperature distribution pattern on a line of the heated joint and determine whether or not the joint is defective based on the temperature distribution pattern.
The soldered joint of the electronic circuit board may include many defects such as bridge, solder ball, void, poor bond, blow hole, insufficient solder, lack of wetting and slippage of lead position. The on-time change of a temperature of one spot and the temperature distribution pattern of a line of a joint heated for a constant time offered by the foregoing prior arts make it possible to determine some kinds of the defects but impossible to determine all kinds of the defects and to generally determine the joint. Hence, the electronic circuit board checked by those prior arts may often become defective when it is built in the product.